This invention relates to insulation panels, and more particularly to insulation panels comprising an exterior gas impermeable barrier enclosing a microporous filler insulation material that supports the outer walls when atmospheric gases are evacuated from the interior of the panel.
Vacuum insulation panels are known for various uses including use in refrigeration appliances where they greatly enhance the degree of thermal insulation within the cabinet of the appliance. Such panels must remain effective for the life of the appliance, generally a period in excess of 20 years. To do so, the panels must be highly gas impervious, yet must be able to prevent transmission of heat not solely by conduction and radiation through the panels, but also by conduction along the surface of the panels. Further, any gases that do permeate the panel walls in excess of what is tolerable, depending on the panel filler insulation material, must be absorbed or otherwise captured to prevent degradation of the panels which, for insulation purposes, are most effective only when the interiors of the respective panels are evacuated of all gases.
Vacuum insulation panels are known such as that disclosed in U.S. Pat. No. 3,179,549 which discloses a conventional single compartment vacuum thermal insulation panel using a microporous-powder or fibrous filler material.
U.S Pat. No. 2,863,179 discloses a multi-compartment insulation material for refrigerators. An inner bag seals a fibrous material in an insulating gas filled environment, and is intended to prevent the insulating gas from escaping. An outer bag contains the inner bag and an adjacent layer of fibrous insulation. The purpose of the outer bag is to prevent moisture and air from entering the inner bag, and to minimize abrasions caused by handling, however, the inner bag is not shielded from atmospheric pressure.
U.S. Pat. No. 4,529,638 discloses a conventional single compartment vacuum thermal insulation panel. The panel has a composite barrier film and a microporous powder filler.
U.S. Pat. No. 4,669,632 discloses a vacuum thermal insulation panel. U.S. Pat. No. 4,683,702 discloses a vacuum thermal insulation panel having multiple internal compartments to facilitate evacuation of the panel. A permeable interior film layer contains the powder filler in one compartment, and the panel is evacuated through the other compartment. The resulting panel has only one main insulating compartment. The extra compartment does not shield the main compartment from atmospheric pressure.
It is important in the construction of vacuum thermal insulation panels to prevent the vacuum within the panels from being lost due to slight permeability of the walls of the panel. Therefore, as is known in the art, "getter" materials are placed within the panel to absorb various gases including oxygen, water vapor, nitrogen, etc. Use of such getter materials in vacuum insulation panels is known and is disclosed in U.S. Pat. Nos. 4,000,246; 4,444,821; 4,668,551; 4,702,963 and 4,726,974. Each of said patents discloses the use of a getter material in a single compartment of a vacuum insulation panel. A problem resulting from the use of such getter materials is that some getter materials may absorb more than one type of gas and thus may be consumed by a relatively prevalent type of gas, such as water vapor and thus would not be available to absorb other gases, while less expensive materials should be used for absorbing water vapor. Once the getter materials have been consumed, degradation of the panel will begin.